Electric motor system.



. D. C. WRIGHT.

ELECTRIC MOTOR SYSTEM.

APPLICATION FILED MAR. 27. 1916.

Patented Dec. 24, 1918.

UNITED STATES ATENT OFFICE.

DAVID C. WRIGHT, 0F WICKLIFFE-ON-THE-LAKE, OHIO, ASSIGNOR TO THEELECTRIC CONTROLLER & MANUFACTURING COMPANY, OF CLEVELAND, OHIO, ACOBPORA- 'IION OF OHIO.

ELECTRIC MOTOR SYSTEM.

Application filed March 27, 1916.

To all whom it may concern:

Be it known that I, DAVID C. lVRIGH'r, a citizen of the United States,residing at lVickliffe-on-the-Lake, in the county of Cuyahoga and Stateof Ohio, have invented new and useful Improvements in Electric MotorSystems, of which the following is a specification. I

This invention relates broadly to electric motor systems, and moreparticularly to such electric motor systems as contain dynamic bra-kingcircuits.

In the operation of motor systems in which the motor is accelerated by aseries of contactors which successively short-circuit resistancesections, and use the same resistance sections or some of them fordynamic braking, it sometimes happens, particularly when the masterswitch is thrown very rapidly from the running position to the dynamicbraking position, that the contactors do not function properly and thestarting and braking currents are not kept within desirable limits. Itis the principal object of this invention toprovide means whereby thecontacts of a final switch which may be closed at the time the masterswitch is moved from the running position to the dynamic brakingposition, will be open-circuited when the master switch is so moved,thereby preventing the establishing of a circuit in parallel with thedynamic braking circuit through the contacts of such switch and thesevere arcing on those contacts when they open. Other objects willappear hereinafter.

Referring to the accompanying drawin Figures 1 and 2 are diagramsillustrating two of the many forms of my invention.

Referring first to Fig. 1, A represents the armature of an electricmotor and F the shunt field Winding thereof; A master controller M,having three operative positions, viz., forward, reverse, and off-brake,

.connects the motor to a source of supply for forward or reverserunning, and disconnects it from the supply and establishes internalconnections for stopping the motor by dynamic braking. The startingresistances R R R and R controlled. by the resistance-controllingswitches S S S and S are provided for accelerating the motor in startingand for gradually bringing it to-rest by dynamic braking when stopping.

Specification of Letters Patent.

Patented Dec. 24, 1918.

Serial No. 86,832.

Any well-known type of resistance-controlllng switch may be used forcontrolling the resistances, but I prefer to employ electromagneticswitches of the type disclosed in Canfields application, Serial Number583,000, filed September 21, 1910, and Eastwoods Patent, No. 1,040,292,issued Octoher 8, 1912, in which the operating windings of the switchesare connected in series with the motor, the switches possessing thepeculiar characteristic of being locked open when the current in thewindings is above a predetermined value, and closing when the current isreduced to that value. In accelerating the motor in either direction theresistance sections R R R and R are all connected in series with themotor, and are then successively short-circuited by the closure of theswitches S S S and S The switches are operated by the windings C C C andC, and the switch S has a shunt holding winding C which merely acts tohold the switch closed after it has been closed by its operating windingC but is not sufficiently strong to close the switch. For stopping themotor by dynamic braking certain of the resistances are reinserted inseries with the armature and short-circuited by the switches as duringacceleration of the motor.

The controller M is provided with a set of stationary contacts 1 to 8,and with three sets of movable contacts; one set of forward runningcontacts 9 to 1 1, one set of reverse running contacts 15 to 20, and oneset of off Or brake contacts 21 and 22. Each set of movable contacts maybe brought separately into engagement with the set of stationarycontacts.

If the master controller M is moved to the forward running position,where the movable set of contacts 9 to 11- engages the sta-' tionary setof contacts 1 to 6, respectively, current flows from the positive linemarked through the master controller contacts 7, 1, 9, 11, and 3 to thewinding C of the switch S all the starting resistance sections R R R andR in series, the armature A, and the master controller contacts 5, 13,12, and 4 t0 the negative line marked The current in this circuit startsthe motor and locks the switch S open. When the motor current falls tothe operating point for which the switch S is set, it closes andshort-circuits the resistance section R and connects the operatingwinding 0 of the switch S in series with the winding C and the contactsof the switch S The rush of current due to the cutting out of the resistance section B locks the switch S open until further acceleration of themotor causes the current to fall to the operating point for which theswitch S is set, whereupon it closes and short-circuits the section R ofthe resistance, and connects the winding C of the switch S in serieswith the windings C and C and the contacts of the switches S and S Therush of current due to the cutting out of the resistance section B locksthe switch S open. When the current has again fallen, the switch Scloses and shortcircuits the resistance section B "and another rush ofcurrent ensues. Finally, when the current has again fallen, due to thefurther speeding up of the motor to the operating point for which theswitch S is set, it closes and short-circuits the section of resistanceR and also short-circuits its own winding C and the windings C C and Cof the switches S S and S by establishing a new circuit through themaster switch from the positive line through the contacts 7, 1, 9, 10,

and 2, and the contacts of the switch S the motor armature A, thecontacts 5, 13, 12, and 4: to the negative line. The closure of theswitch S by connecting its contacts directly to the positive line asabove de scribed, connects the holding winding C directly to thepositive line through the contacts of the switch S, the current flowingfrom the positive line through the winding 0, and the contacts 6, 14,12, and 1, to the negative line. The current in the winding holds theswitch S closed, which shortcircuits the windings of the switches S Sand S which immediately open.

If, however, the master cont-roller M is moved to the reverse runningposition, so that the movable set of contacts 15 to 20 engagescorresponding contacts of the stationary set 2 to 7 circuits will beestablished to cause the direction of the flow of current through theresistance sections and the switches and the armature to be reversed,whereupon the motor rotates in the reverse direction, as is readilyapparent from the drawing.

If the master controller is moved from either the forward or reversepositions to the off, or brake, position, the motor sys tem will bedisconnected from the source of supply except as to the field winding F,and a dynamic braking circuit for the motor will be established, themotor acting as a generator with a closed path from one side of thearmature A, through the contacts 5, 21, 18, 22, and 8, the winding 0 ofthe switch S the resistance sections R R and R in series, and back tothe other side of the armature A. It will be noted that the firstsection R is not included in this circuit. The current in the lattercircuit locks the switch S open. When the current falls, due to theslowing down of the motor to the operating point for which the switch Sis set, it closes and short-circuits the resistance section R andconnects the winding C of the switch S in series with the winding C andthe contacts of the switch S thereby locking open the switch S When thecurrent again falls to the operating point of the switch S it closes andshort-circuits the resistance section B and connects the winding 0 ofthe switch S in series with the windings C and C and the contacts of theswitches S and S and locks the switch S open. When the current againfalls to the operating point for which the switch S5 is set, this switchcloses, but the path of the current does'not change because one of thecontacts of the switch S is open on the master controller at 2.Therefore, on the closure of the switch S the resistance section Rremains in the dynamic braking circuit. The winding C of the switch Sand the holding winding C of the switch S are not energized, theircircuits being open respectively at 3 and 6 on the master controller M.As the motor slows down, the dynamic braking current becomes so smallthat the switches S S and S fall open.

During the acceleration of the motor the four resistance sections areall connected in 00 series with the motor and then successivelyshort-circuited; while for dynamic braking, the sections R R and R onlyare connected in circuit with the motor and of these the sections R andB only are short circuited.

It has been common practice to employ all of the accelerating switchesfor dynamic braking, which is unsatisfactory because the currentrequirements of starting and braking are diiferent. In such practice ithas been essential that the master switch be moved from the running tothe braking position, or from the forward to the reverse positionthrough the braking position, slowly so that the final acceleratingswitch shall have time to open before the master switch reaches thebraking position; otherwise, all of the braking resistance would beshort-circuited permanently by the final switch, and the motor might beinjured by a rush of excessive braking current, or, at best, the finalswitch would open late and draw a destructive arc on its contacts. Bycontrollin the dynamic braking resistance as described, I obtainsatisfactory braking current, reduce the tendency to spark or flash onthe motor brushes, eliminate the danger of a current overload on themotor, and bring the motor to rest in a safe and efficient manner. By

causing all of the switches but the'last to be open prior to dynamicbraking, and by opening the circuit of the contacts of the final switchon moving the master switch to the dynamic braking position, I makecertain that the dynamic brakingresistance is all inserted in the motorcircuit when :the master switch-is moved to or through the brakingposition, no matter how rapidly it may be moved.

In special applications in which the re quirements of dynamic brakingcurrent "approach more nearly to those of starting current, I find itadvisable to'employ all ofthe starting resistance for dynamic brakingpurposes. In Fig. 2Ishow .a diagram of a system, so employing thestarting resistance.

When the master switch in Fig; 2 is thrown to the oil Orbrake' position,the dynamic braking circuit for the motor is established from thearmature A through the contacts 5, 21, 18, 22, and 8, the winding C ofthe switch S the resistance sections R R R and R in series, and back tothe armature A. The resistance section R as well as the sections R R andR, is now included in the circuit. The current in this circuit locksopen the switch S and when the current falls due to the slowing down ofthe motor to the operating point for which the switch S is set, thisswitch closes, short-circuits the resistance section B, and connects thewinding C of the switch S in series with the winding C and the contactof the switch S causing the switch S to be locked open. The remainder ofthe braking operation is the same as that described in connection withFig. 1. The resistance sections R R R and R are connected in series fordynamic braking, and the sections R R and R successively cut out, Bbeing left in the circuit by the opening of the circuit of the contactsof the switch S at the master switch M, all as is readily understood.

I have illustrated my invention in connection with a reversing masterswitch, but it will be understood that the invention may be practisedwith a non-reversing master switch; that any number and any suitableform of resistance switches and any suitable form of master switch maybe employed in the practice of my invention, and I do not, therefore,wish to be limited to the forms which I have illustrated.

I claim 1. In a motor system, an electric motor, a circuit therefor,resistance sections in the circuit, switches operated in sequence forsuccessively short-circuiting the resistance sections, means forconnecting the armature and some of the resistance in a dynamic brakingcircuit, and means whereby, when the armature of the motor and any ofthe said resistance sections are connected in a dynamic braking circuit,the circuit through the contacts of the final switch is open though thesaid contacts are closed.

2. In a motor system, a motor, acircuit therefor, resistance sections inthe circuit, switches operated in sequence. for successivelyshort-circuiting the resistance sections,'means for connecting thearmature of the motor and some of the resistance sections in a dynamicbraking circuit, and means whereby,1when the dynamic braking connectionsare established, thecir'cuit through the contacts of the final switch isopen though the said contacts are closed. I

3. In a motor system, a circuit there? for, resistance sections,.electro-magnetic switches operatedin sequencefor short-circuiting theresistance sections successively, and means for-connecting the motor andall of'the resistance sections in the circuit to start the motor andaccelerate it to normal speed, and for connecting the armature andcertain of the said resistance sections in a dynamic braking circuit andsimultaneously opening the circuit through the contacts of the finalswitch though the said contacts are closed.

4. In a control-system for electric motors, an electricinotor, a circuittherefor, sections of resistance in the circuit, successivelyoperatingelectro-magnetic switches for successively cutting out the sections ofresistance from the circuit, means for including certain sections of theresistance, including the final section, in a dynamic braking circuit,and means for retaining the final section of dynamic-braking resistancein the braking circuit when the final switch closes.

5. In a motor control system, a motor, a motor circuit, a resistance insaid circuit, a plurality of switches for starting the motor and forstopping it by dynamic braking, all of said switches being arranged inthe circuit to close successively and start the motor by reducing thesaid resistance in said circuit and some of the switches being arrangedto close successively and stop the motor by reducing the said resistancein said circuit, and means whereby the circuit through the contacts ofthe final switch are out of electrical connection with one terminal ofthe motor during the stopping of the motor whereby the closure of thefinal switch does not reduce the resistance in the circuit.

6. In a motor control system, a motor, a motor circuit, a resistance inthe circuit, a plurality of electro-magnetic switches for starting themotor and for stopping it by dynamic braking, arranged to be closed bythe armature current of the motor, the contacts of all the switchesbeing arranged in the circuit to start the motor by reducing the saidresistance, and the contacts of some of the switches being arranged inthe motor circuit to stop the motor by reducing the said resistance, andmeans for disconnecting the contacts of the final switch from oneterminal of the motor 7. In a motor control system, a motor, a motorcircuit, a resistance in said circuit, a plurality of switches forstarting the motor andfor stopping it by dynamic braking, all of saidswitches being arrangedin thecircuit to :start the motor by reducing theamount of resistance in said: circuit 'andsome ofthetswitches beingarranged to stop.

the motor,-and,means whereby the contacts of the last switch toclosevduringdynamic braking" are always ropen-circuited during dynamicbraking. i

8. In a motor control system,'-a motor, a'

0010108 0! thin patent in, he obtained 16': fiye cents each,;byaddressing the Gommissioner of Patents, I

starting circuit and a dynamic braking circuit therefor, a master forselectively establishing said circuits, a resistance, a plurality ofswitches arranged to close successively,

each of said switches onclosing reducing the amount of resistance 1nsaid circuit to startthe motor, and two or more of said SWltChBS Signedat Cleveland Ohio this 23rd day ofMarch, A. D. 1916.

' DAVID o. WRIGHT.

v Washington, 13.0."

